Field of the Invention
The invention relates to a stand-alone functional apparatus for use in consumer products, which comprises a control circuit in the form of a microcomputer, and a non-volatile memory for storing status data.
The term "stand-alone" is to be understood to mean that the functional apparatus can operate independently, without being subordinate to an external device, thus one that does not operate like a peripheral apparatus which is subordinate to a central computer.
Description of the Prior Art
In its generality, a stand-alone functional apparatus comprises a plurality of independent or mutually cooperating processing circuits, whose operation is controlled by the control circuit. They receive status data from the control circuit or apply status data thereto. These status data are indicative of the state in which a processing circuit is or to which state it must adjust itself. In a TV-receiver they represent, for example, the channel or program number the set is tuned to, or tone control, volume, luminance, contrast, etc.
To render it possible to apply the correct status data to the different processing circuits, a plurality of control circuits are coupled to the microcomputer and the microcomputer comprises an internal non-volatile memory having a plurality of addressable memory locations which are each addressable by means of a program counter. Each memory location comprises a given processing stage which is represented by a predetermined code word. A group of mutually associated processing steps is called a control program. The number of such control programs stored in the internal nonvolatile memory differs greatly from apparatus to apparatus.
Although microcomputers are very suitable for use as a control circuit, the mode of operation of the most contemporary microcomputers has been found to be far from reliable when they are used in an environment in which an electromagnetic field is present which may change considerably. Such a situation occurs, for example, in television receivers. As is known, there is a voltage of approximately 25,000 Volts between the anode and the cathode of the picture tube of a TV-receiver. Breakdown phenomena may occur due to contaminations in the picture tube. Such a breakdown phenomenon may be considered to be a current pulse which has a rise time of approximately 5 nanoseconds, a peak value of approximately 220 Amp. and a duration of approximately 100 nanoseconds. Such a current pulse generates voltage pulses everywhere in the TV-receiver and consequently also in the microcomputer. This may result in the microcomputer arriving in an undefined state, because the content of one or more internal registers of the microcomputer such as the program counter, stack pointer, volatile memory, gate registers, etc. has changed and the new contents are not associated with each other. The normal functioning of the microcomputer and consequently also the normal functioning of the functional apparatus is seriously disturbed thereby. With a TV-receiver this usually results in the picture disappearing completely and the microcomputer no longer responding to changes in the states of processing circuits and control circuits, which gives the user the impression that the TV-receiver is defective.